Method and apparatus for indicating a temporary block flow to which a piggybacked ack/nack field is addressed

ABSTRACT

A method and an apparatus for indicating a temporary block flow (TBF) to which a piggybacked acknowledgement/non-acknowledgement (PAN) field is addressed. A method and apparatus of performing receive processing to reduce the probability of false acceptance of erroneous PANs are also disclosed. A transmit station generates a PAN check sequence (PCS) and performs a channel coding on a PAN field and the PCS. The transmit station scrambles the encoded bits of the PAN field and the PCS with a TBF-specific scrambling code. Because of the scrambling, the PCS decoding at a receive station will pass if the data block is received by an intended receive station, while the PCS decoding will fail if received by a non-intended receive station. Alternatively, the scrambling may be performed before the channel coding. Alternatively, the transmit station may combine the PAN field and a temporary flow identity (TFI) to generate a PCS.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/651,868 filed Oct. 15, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/106,138 filed Apr. 18, 2008, which issued asU.S. Pat. No. 8,296,619 on Oct. 23, 2012, which claims the benefit ofU.S. provisional application Nos. 60/913,179 filed Apr. 20, 2007,60/974,293 filed Sep. 21, 2007, and 60/981,980 filed Oct. 23, 2007, thecontents of which are hereby incorporated by reference herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

Latency reduction is one of the considerations in a GSM/EDGE radioaccess network (GERAN). Two techniques have been proposed for latencyreduction: reduced transmission time interval (RTTI) and fastacknowledgement/non-acknowledgement (ACK/NACK) reporting (FANR).

Conventionally, an ACK/NACK report is sent in an explicit message, alsoreferred to as a radio link control/medium access control (RLC/MAC)control block. The ACK/NACK report is addressed to a particular radioresource, called a temporary block flow (TBF).

A TBF is a temporal connection between a mobile station and a network tosupport a uni-directional transfer of data. A TBF is temporary andmaintained only for the duration of the data transfer. Each TBF isassigned a temporary flow identity (TFI) by the network. The TFI isunique among concurrent TBFs in each direction and is used instead ofmobile station identity in the RLC/MAC layer. The same TFI is includedin every RLC header belonging to a particular TBF.

It has been proposed to send the ACK/NACK report for a certain TBF as a“piggyback” on an RLC/MAC data block that may be addressed to anotherTBF. The field that carries the ACK/NACK report is referred to as apiggybacked ACK/NACK (PAN) field.

Since the PAN field is included in a data block that may be addressed toa different TBF, it is necessary to identify to which TBF the PAN fieldis addressed. Various proposals have been made to identify the correctTBF in the PAN field, including using a TFI or an uplink (UL) state flag(USF). During establishment of the uplink TBF, a USF is assigned to eachmobile station. The USF is used by the network to indicate which mobileterminal is allowed to transmit in the following uplink radio block.

In either case, some number of bits, (typically ranging from three tofive), should be dedicated to the TBF identity in the PAN field. Itwould be desirable to have an efficient method of sending the TBFidentity in the PAN field such that no dedicated bits are needed toidentify the TBF.

SUMMARY

A method and an apparatus for sending and receiving a PAN are disclosed.A method and apparatus for indicating a TBF to which a PAN field isaddressed are also disclosed. a receiving process which greatly reducesprobability of false acceptance of erroneously received PANs while notreducing probability of accepting correctly received PANs is alsodisclosed. A transmit station generates a PAN check sequence (PCS) andperforms a channel coding on the PAN field and the PCS. In a secondvariant the transmit station scrambles the encoded bits of the PAN fieldand the PCS with a TBF-specific scrambling code. Because the PAN fieldand the PCS are scrambled with a TBF-specific scrambling code, the PCSdecoding at a receive station will pass if the data block is received byan intended receive station, while the PCS decoding will fail ifreceived by a non-intended receive station. In a third variant, thescrambling may be performed before the channel coding. For all threevariants the transmit station may combine the PAN field and a TFI togenerate the PCS. In addition, advanced receiver techniques are definedwhich significantly improve the reliability of the processing. For aspecified format for encoding the PAN field, the PCS and the TBF, theuse of forward error correction filtering greatly reduces theprobability of false acceptance of an invalid PAN while not reducing theprobability of acceptance of correctly received PAN transmissions. Theseimprovements are achievable independent of whether or not the scramblingcode is applied to the PAN and also independent of whether or not thePCS is dependent or independent of the TBF.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows an example radio block;

FIG. 2 is a block diagram of an example transmit station in accordancewith one embodiment;

FIG. 3 is a block diagram of an example receive station in accordancewith one embodiment;

FIG. 4 shows a receive station in accordance with another embodiment;

FIG. 5 shows a receive station in accordance with another embodiment;

FIG. 6 is a block diagram of an example transmit station in accordancewith another embodiment;

FIG. 7 is a block diagram of an example receive station that correspondsto the transmit station of FIG. 6; and

FIG. 8 shows simulation results comparing the advanced receiveprocessing with the conventional receive processing.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 1 shows an example radio block 100. The radio block 100 for datatransfer includes one RLC/MAC header 102, a header check sequence (HCS)104, one or more RLC data block(s) 106, a block check sequence (BCS)108, a PAN field 110, and a PCS 112. The RLC/MAC header 102, the RLCdata block(s) 106 and the PAN field 110 are coded separately for errordetection and correction, and a separate checksum, (e.g., a cyclicredundancy check (CRC) checksum), is attached to each of them. TheRLC/MAC header 102 contains a control field indicating whether a PANfield 110 is included or not in the radio block 100. The HCS 104 is usedfor error detection of the RLC/MAC header 102. The BCS 108 is used forerror detection of the RLC data block 106. A separate BCS may beincluded for each RLC data block. The PAN field 110 containspiggy-backed ACK/NACK information sent in one direction to provideacknowledgement for a TBF in the other direction. The PCS 112 is usedfor error detection of the PAN field 110.

FIG. 2 is a block diagram of an example transmit station 200 inaccordance with one embodiment. The transmit station 200 may be a WTRUor a base station. The transmit station 200 includes a PCS generator202, a channel coding unit 204, a scrambling code generator 206(optional), an adder 208 (optional), and a transceiver 210. A PAN fieldis encoded separately from the header and the payload of the RLC data.The PCS generator 202 computes a PCS with the PAN field. For example,the PAN field may be 20 bits and the PCS may be 10 bits. The channelcoding unit 204 performs channel coding with the PAN field and the PCS.For example, the channel coding may be ⅓ forward error correction (FEC)coding to generate 90 bits of output from the 30 bits of PAN field andthe PCS. The encoded bits may be punctured to 80 bits.

The scrambling code generator 206 may generate a TBF-specific scramblingcode based on the TFI. The length of the scrambling code may be equal tothe number of the channel coded bits. In the above example, thescrambling code may be 80-bits long. A unique scrambling code isgenerated for each value of TBF. The scrambling codes may be orthogonalto each other. The scrambling codes are designed to have large minimumdistances.

The channel coded bits may then be scrambled, (i.e., modulo 2 added bythe adder 208), with the TBF-specific scrambling code. A data blockincluding the scrambled encoded bits is transmitted by the transceiver210.

FIG. 3 is a block diagram of an example receive station 300 inaccordance with one embodiment. The receive station 300 may be a WTRU ora base station. The receive station 300 includes a transceiver 301, ascrambling code generator 302 (optional), an adder 304 (optional), achannel decoding unit 306, and a PCS decoder 308. The transceiver 301receives a data block including scrambled coded bits of a PAN field anda PCS. The scrambling code generator 302 generates a TBF-specificscrambling code based on the TFI. The received scrambled coded bits ofthe PAN field and the PCS are descrambled, (i.e., modulo-2 added to theTBF-specific scrambling code by the adder 304). The channel decodingunit 306 decodes the descrambled coded bits to obtain the PAN field andthe PCS. The PCS decoder 308, (e.g., CRC decoder), then performs PCSchecking with the received PAN field and PCS. If the PCS checkingpasses, the received PAN field is accepted, but if the PCS checkingfails, the received PAN field is rejected. Because the PAN field and thePCS are scrambled with a TBF-specific scrambling code, the PCS decodingwill pass if the data block is received by an intended receive station,while the PCS decoding will fail if the data block is received by anon-intended receive station.

FIG. 4 shows a receive station 400 in accordance with anotherembodiment. The receive station 400 includes a transceiver 401, ascrambling code generator 402 (optional), an adder 404 (optional), achannel decoding unit 406, a PCS decoder 408, and a comparator 410. Theembodiment disclosed herein may be implemented with or withoutscrambling. The transceiver 401 receives a data block including(scrambled or unscrambled) coded bits of a PAN field and a PCS. Thescrambling code generator 402 may generate a TBF-specific scramblingcode based on the TFI (if applicable). The received coded bits of thePAN field and the PCS may be descrambled, (i.e., modulo-2 added to theTBF-specific scrambling code by the adder 404) (if applicable). Thechannel decoding unit 406 decodes the coded bits to obtain the PAN fieldand the PCS.

In order to achieve better performance of PAN field error detection thanthe conventional CRC-based error detection mechanism, the receivestation 400 may make use of soft metrics to estimate how well thechannel decoding performs. The comparator 410 may compare a soft metriccomputed by the channel decoding unit 406 to a threshold. If the channellink quality is evaluated to be bad based on the soft metrics, thereceive station 400 may reject the received PAN field before the PCSdecoding.

For example, for Viterbi-type FEC decoders, the soft metric may be thebest survivor path metric, (which measures the error between thereceived sequence and the estimated optimal path). The best survivorpath metric, (either highest or lowest depending on the decodingalgorithm), is compared to the threshold and the PAN field may bediscarded based on the comparison result.

Alternatively, the soft metric may be the difference between the bestand the second best survivor path metrics, or the difference between thebest and the worst survivor path metrics. If the received signal ishighly corrupted by the channel, the surviving paths are likely to beclose to each other and the dynamic range of the path metric differencesis likely to be small. On the other hand, the metric is likely to belarger if the signal corruption by the channel is marginal. Thedifference is compared to a threshold and the PAN field may be discardedif the difference is less than, (or greater than depending on thedecoding algorithm), the threshold.

The PCS decoder 408, (e.g., CRC decoder), then performs PCS checkingwith the received PAN field and PCS. If the PCS checking passes, thereceived PAN field is accepted, but if the PCS checking fails, thereceived PAN field is rejected.

FIG. 5 shows a receive station 500 in accordance with anotherembodiment. The receive station 500 includes a transceiver 501, ascrambling code generator 502 (optional), an adder 504 (optional), achannel decoding unit 506, a PCS decoder 508, a bit error counter 510,and a comparator 512. The embodiment disclosed herein may be implementedwith or without scrambling. The transceiver 501 receives a data blockincluding (scrambled or unscrambled) coded bits of a PAN field and aPCS. The scrambling code generator 502 may generate a TBF-specificscrambling code based on the TFI (if applicable). The received codedbits of the PAN field and the PCS may be descrambled, (i.e., modulo-2added to the TBF-specific scrambling code by the adder 504) (ifapplicable). The channel decoding unit 506 decodes the coded bits toobtain the PAN field and the PCS.

The bit error counter 510 calculates the number of bit errors. Thecomparator 512 compares the calculated bit error counts to a threshold.The bit error counts may be calculated by comparing re-encoded PAN fieldand PCS bits, (i.e., re-performing FEC encoding on the FEC decoded PANfield and PCS bits), with the input of the channel decoder 506, (i.e.,hard decision or soft decision bits (after descrambling if applicable)).The received PAN field is rejected if the computed bit error counts aregreater than the threshold.

FIG. 6 is a block diagram of an example transmit station 600 inaccordance with another embodiment. In this embodiment, the scramblingmay be performed before channel coding. The transmit station 600includes a PCS generator 602, a scrambling code generator 604(optional), an adder 606 (optional), a channel coding unit 608, and atransceiver 610. The PCS generator 602 generates a PCS with the PANfield. The scrambling code generator 604 generates a TBF-specificscrambling code based on the TFI. For example, if the PAN field istwenty bits and the PCS is 10 bits, the TBF-specific scrambling code of30 bits may be generated to scramble the PAN field and the PCS. Anyconventional coding may be used to map a 5-bit TFI into a thirty bitscrambling code. A good set of codes will have the largest possibleminimum distance and the lowest frequency of occurrence of this minimumvalue. Under these conditions, the probability of erroneously acceptinga PAN field addressed to another station will be minimized.

The scrambling code is modulo-2 added to the PAN field and the PCS bitsby the adder 606. The scrambled PAN field and PCS bits are channel codedby the channel coding unit 608. The channel coded bits are thentransmitted by the transceiver 610. This embodiment has an advantagethat the scrambling sequence length is smaller and that channel errorsare corrected by the channel coding, (i.e., FEC).

FIG. 7 is a block diagram of an example receive station 700 thatcorresponds to the transmit station of FIG. 6. The receive station 700includes a transceiver 701, a channel decoder 702, a scrambling codegenerator 704 (optional), an adder 706 (optional), and a PCS decoder708. The transceiver 701 receives a data block including coded bitsgenerated from the scrambled PAN field and PCS. The channel decoder 702decodes the channel coded bits to recover the scrambled PAN field andPCS. The scrambling code generator 704 generates a TBF-specificscrambling code based on the TFI. The scrambling code is modulo-2 addedto the scrambled PAN field and PCS by the adder 706 to recover theunscrambled PAN field and PCS. The PCS decoder 708 then performs PCSchecking with the unscrambled PAN field and PCS. If the PCS checkingpasses, the received PAN field is accepted, but if the PCS checkingfails, the received PAN field is rejected.

The receive station 700 may optionally include a comparator forcomparing soft metrics with a threshold, similar to the receive station400 in FIG. 4, and may optionally include a bit error counter and acomparator for calculating and comparing a bit error count to athreshold, similar to the receive station 500 in FIG. 5. It should benoted that the scrambling scheme is optional and the advanced receivertechnique (soft metric receive processing) may be implementedindependent of the scrambling feature.

In accordance with another embodiment, the TFI, (e.g., 5 bits long), maybe combined with the PAN field, and the PCS may be calculated with thecombined PAN field and TFI. After computing the PCS, the TFI is removedand the PAN field and the calculated PCS are channel coded andtransmitted. The receive station inserts its own TFI into the decodedbits after channel decoding. The receive station then performs PCScheck. An intended receive station will pass the PCS check, while anon-intended receive station will introduce a burst of errors of five(5) or fewer bits by inserting its TFI. Since 10-bit hh is capable ofdetecting all bursts of errors less than 11 bits, the non-intendedreceive station will fail the CRC check and reject the PAN message withvery high probability.

The schemes of using soft metrics disclosed above are based on animplicit assumption that the FEC decoder produces hard decision outputs,(e.g., quantized binary outputs). The schemes can be extended to thecase when the FEC decoder produces soft decision outputs. For example,the FEC decoder may produce a bit error probability (BEP), which is anestimate of the reliability of the decoded bits. Such a soft metric maybe directly used to assist the PAN detection process, as describedabove.

The receiver embodiments of using soft metrics from the decoder asdescribed with reference to FIGS. 4 and 5 are applicable to anytransmitter-receiver implementations, and are not limited to thetransmitter-receiver implementation disclosed herein. For example, thesoft metric receive processing (the receive processing scheme disclosedwith reference to FIGS. 4 and 5) may be applied to the case where thetransmitter sends PAN fields wherein a PCS is masked with a TFI, asdisclosed in U.S. patent application Ser. No. 12/056,433 entitled“METHOD AND APPARATUS FOR INDICATING A TEMPORARY BLOCK FLOW TO WHICH APIGGYBACKED ACKNOWLEDGEMENT/NON-ACKNOWLEDGEMENT FIELD IS ADDRESSED.”

FIG. 8 shows simulation results comparing the soft metric receiveprocessing with the conventional receive processing. In the simulation,the scrambling is turned off and CRC TFI masking and the soft metricreceive processing are implemented. The estimated raw bit errors areused as the soft metric. Three cases are considered as follows:

-   -   (A) 20 bit Payload+10 bit CRC→80 raw bits (Baseline);    -   (B) 20 bit Payload+8 bit CRC→80 raw bits; and    -   (C) 20 bit Payload+8 bit CRC→(80−n) raw bits, n=1, 2, . . , 5.        For the cases (B) and (C), the soft metric receive processing is        applied.

Two performance metrics are measured as follows:

-   -   (1) 1-Pr(Correct Acceptance) for the intended WTRU versus SNRs        from −0.6 dB to 2.4 dB; and    -   (2) Pr(False Acceptance|Erraneous Decoded Block) for both        intended and unintended WTRUs for −0.6 dB.

At −0.6 dB, the thresholds for soft metric filtering were chosen to havethe same or similar Pr(False Acceptance I Erraneous Decoded Block) forall three cases as shown in Table 1.

TABLE 1 (B) threshold = (C) threshold = (A) 20, n = 0 18, n = 4 Pr(False1.01 × 10⁻³ 1.08 × 10⁻³ 1.00 × 10⁻³ Acceptance | Erraneous DecodedBlock)

As shown in FIG. 8, the soft metric receive processing may increase theprobability of correct acceptances for the intended users by about 0.25dB, or reduce the PAN raw bits by 4 bits, with the same or similarprobability of false acceptance as the baseline approach.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

What is claimed is:
 1. A method for processing a received data block,the method comprising: receiving a data block including coded bits of afirst field and a second field, wherein the second field is a cyclicredundancy check (CRC) checksum of the first field; decoding the codedbits of the first field and the second field; performing a metric testby comparing a metric computed during the decoding of the coded bitswith a threshold; performing a CRC test; and determining that the firstfield is properly decoded on a condition that a result of the metrictest and a result of the CRC test are acceptable.
 2. The method of claim1 wherein the metric is a best survivor path metric in Viterbi-typeforward error correction decoding.
 3. The method of claim 1 wherein themetric is a difference between a best survivor path metric and a secondbest survivor path metric in Viterbi-type forward error correctiondecoding.
 4. The method of claim 1 wherein the metric is a bit errorrate.
 5. The method of claim 1 wherein the first field is a piggybackedacknowledgement/non-acknowledgement (PAN) field included in a data blockto indicate either an acknowledgement (ACK) or a non-acknowledgement(NACK).
 6. The method of claim 1 further comprising: descrambling thecoded bits with a scrambling code.
 7. An apparatus for processing areceived data block, the apparatus comprising: a receiver configured toreceive a data block including coded bits of a first field and a secondfield, wherein the second field is a cyclic redundancy check (CRC)checksum of the first field; a decoder configured to decode the codedbits of the first field and the second field; a metric test unitconfigured to perform a metric test by comparing a metric computedduring the decoding of the coded bits with a threshold; and a CRCdecoder configured to perform a CRC test, wherein the first field isdetermined to be properly decoded on a condition that both a result ofthe metric test and a result of the CRC test are acceptable.
 8. Theapparatus of claim 7 wherein the metric is a best survivor path metricin Viterbi-type forward error correction decoding.
 9. The apparatus ofclaim 7 wherein the metric is a difference between a best survivor pathmetric and a second best survivor path metric in Viterbi-type forwarderror correction decoding.
 10. The apparatus of claim 7 wherein themetric is a bit error rate.
 11. The apparatus of claim 7 wherein thefirst field is a piggybacked acknowledgement/non-acknowledgement (PAN)field included in a data block to indicate either an acknowledgement(ACK) or a non-acknowledgement (NACK).
 12. The apparatus of claim 7further comprising: a descrambler configured to descramble the codedbits with a scrambling code.